1. Technical Field
The present invention relates to toposcopic or everting catheters and methods of fabrication of such catheters. The present invention is an improvement of the catheters and fabrication techniques described in U.S. patent application Ser. No. 06/022,219, now U.S. Pat. No. 4,437,857, filed Mar. 19, 1979 by Seth Goldstein and Robert Jones, and entitled "Method and Apparatus For Traversing Blood Vessels". The subject matter of that prior application is expressly incorporated herein, in its entirety, by this reference.
2. Discussion Of The Prior Art
A prior art everting catheter tube assembly is illustrated in FIG. 1 wherein a primary catheter tube 10 has a highly flexible thin-walled everting catheter tube 11 secured thereto. More specifically, the head or forward end of the everting catheter tube 11 is folded over the open distal end of primary catheter tube 10 and a short length 12 of the everting catheter tube is sealed upon or bonded to the outer circumference of the primary catheter tube. The annular space 14 between the exterior surface of everting catheter tube 11 and the interior surface of primary catheter tube 10 may be supplied with pressurized fluid to force eversion of the catheter tube out through the distal end 15 of the primary catheter tube 10. The everting catheter tube 11, when so everted, effectively rolls along the interior walls of a blood vessel or other anatomical passage.
Another prior art everting catheter assembly is illustrated in FIG. 2 wherein a short length 13 at the head end of everting catheter tube 11 is secured to the interior surface of primary catheter tube 10. The open head end 16 of everting catheter tube 11 faces in the same direction as the open distal end of primary catheter tube 10. As illustrated in FIG. 3, when pressurized fluid is applied to the annular space between the everting catheter tube 11 and the primary catheter tube 10, tube 11 advances as a function of the applied pressure, causing the inner tube to turn inside out upon itself (or evert) and unroll beyond the bond position 13 through the open end 15 of the primary catheter tube.
In both prior art embodiments the opposite end of the inner or everting tube 11 (i.e., the tail end, not illustrated in FIGS. 1-3), being unattached to the primary catheter tube, is dragged forward within the primary catheter tube. In addition, for any everted length of everting catheter 11, the everting pressure within the annular region 14 may be removed and a negative pressure, or vacuum, may be applied to the annular region 14 instead. This vacuum or low pressure is not sufficient to collapse the more rigid conventional catheter 10 but is sufficient to draw the flexible thin-walled everting catheter tube 11 radially outward to an open position. The open everting catheter tube becomes a lumen for infusion and aspiration through the total catheter assembly (assuming that the tail end of the everting tube is appropriately configured).
The prior art techniques for bonding the head end of the everting catheter tube 11 to the primary catheter tube 10 result in serious problems. In the embodiment of FIG. 1, the toposcopic or everting tube 11 is strained considerably during the bonding process, often causing rupture of the everting catheter tube during pressurization of the annular region 14. During clinical use a radiologist often reconfigures the catheter tip by "heat setting" a desired radius or bend in that tip. This "heat set" is also applied to the bond, due to its location at the tip. The heat generated during this process degrades the strength of the bond and the everting tube 11 itself.
In the embodiment illustrated in FIG. 2, the annular pressures required to initiate eversion and to overcome the restriction of a double wall thickness during eversion are very high and, therefore, often lead to failure of the everting catheter element. Moreover, a tearing stress exists on the bond due to the tendency of the bonded wall to evert with the tail of the toposcopic or everting element. In both embodiments the toposcopic element is thermally degraded during the bonding process.
In addition to the problems associated with the bonding techniques employed at the head end in prior art everting catheter assemblies, the tail end configuration of prior art assemblies also has disadvantages. Specifically, the prior art tail configuration generally comprises a complex of tubes, sleeves and mechanical screw fittings which are intended to seal the lumen from the annular region 14 and prevent reverse eversion of the everting element and to provide a rigid metal extension tube for the tail of the everting element. The metal extension was deemed necessary in order to seal the annular space 14.
In order to accommodate these structural elements and their movement, it was necessary to employ a large diameter tube appended to the smaller conventional catheter tube 10 at the proximal end of that catheter tube. This large tube, by necessity, contained an unrestrained length of the tail of the toposcopic element. Lumen infusion pressures required for clinical use of the catheter easily burst the thin-walled toposcopic element where it is unrestrained. that portion of the toposcopic or everting element contained within the conventional catheter is restrained by the catheter.
Another problem associated with prior art everting catheter assemblies relates to filling the narrow annular passage region 14 with sterile media. Specifically, the closed annular space 14 is pressurized to permit the everting catheter 11 to evert. Since the distal or everted-most end of the everting catheter 11 is sealed at the time the region 14 is pressurized, and since complete filling of the region 14 is required for optimal everting and safety in the event of an annular rupture, it is necessary to remove the pre-existing nonsterile fluid from the leading end of the annular region as the pressurized sterile media travels toward that leading end. There is no acceptable apparatus or procedure for accomplishing this in the prior art.